The cationic electrodeposition painting is superior to the commonly used anionic electrodeposition painting in rust resistance of painted material, and has recently been increasingly used in the field of painting for automobile and other fields.
There have been proposed various resin compositions to be used for such cationic electrodeposition painting. However, practically used resin compositions are water-dispersible resin compositions disclosed, for example, in Japanese Patent Laid-open Specification Nos. 51,924/73 and 126,225/76, which are produced by a method wherein an epoxy resin consisting of a bisphenol A/epichlorohydrin condensate is reacted with a primary amine or secondary amine, the aminated epoxy resin is reacted with a partially blocked polyisocyanate, and the reaction product is made into water dispersible.
However, such blocked polyisocyanate type hardenable cationic electrodeposition paint has serious drawbacks that the paint is higher in baking temperature and is larger in the amount of generating tar than the conventional anionic electrodeposition paint.